1. Technical Field
The invention relates to an endless belt, a method of production thereof, and an image forming apparatus.
2. Related Art
In an image forming apparatus by means of an electrophotographic process, an image is formed as follows. First, a surface of the latent image holding member comprising a photoconductive photoreceptor made of an inorganic material or an organic material is charged. Thereafter, laser light obtained by modifying an image signal is irradiated on a surface of the latent image holding member surface to form an electrostatic latent image. Subsequently, a charged toner is used to develop the electrostatic latent image to form a toner image. Finally, the toner image on a surface of the latent image holding member is transferred directly or through an intermediate transfer body onto a recording medium such as paper, followed by fixing to form the image.
Here, as an intermediate transfer belt that is used in an image forming apparatus that adopts a process where a toner image on a photoreceptor is first transferred onto an intermediate transfer body, followed by secondarily transferring a toner image on the intermediate transfer body onto a recording medium such as paper (so-called intermediate transfer process), for instance, a belt that uses polycarbonate (PC), a belt that uses polyvinylidene fluoride (PDDF), a semiconductive (105 to 1011 Ωcm) endless belt in which in a thermoplastic resin such as a blend of polyalkylene terephthalate, an ethylene-tetrafluoroethylene copolymer (ETFE) and PC, a conductive agent such as carbon black or the like is dispersed, or a reinforcement member-containing elastic belt in which a woven fabric made of polyester or the like and an elastic material such as nitrile butadiene rubber (NBR) or the like are laminated are proposed.
Furthermore, recently, a method where the intermediate transfer body is heated to fix a toner image on a recording medium, more specifically, an intermediate transfer/fixing process has also been proposed.
An intermediate transfer/fixing process is a process where, after a toner image on a photoreceptor is secondarily transferred through an intermediate transfer body on a recording medium, the intermediate transfer body is directly or indirectly heated to fix the toner image on the recording medium in contact with the intermediate transfer body. The process has an advantage in that, in comparison with a conventional device where an intermediate transfer unit and a fixing unit are separated, a device may be miniaturized and the cost may be reduced.
Here, a belt material that is used in the intermediate transfer/fixing process is required to have the mechanical strength capable of withstanding stress at the time of driving and simultaneously to be capable of withstanding heat close to 200° C., which is provided at the time of fixing.
On the other hand, in a fixing, process that is carried out at the final step of printing/copying of an image forming apparatus such as an electrophotographic copier, a facsimile, a printer and so on, it is necessary that a toner on a surface of a recording medium such as transfer paper or the like is heated and melted to fix the toner on the surface of the recording medium. In such a fixing process, in place of a conventional hot roll (roller) fixing process, a belt fixing process superior in shortening start-up time is widely in use.
A belt fixing process is a process where, through a film-shaped endless belt, a heater heats a toner on a surface of a recording medium. In the process, a fixing belt and a rubber roll are brought into contact under pressure to form a contact portion, a recording medium on which a toner image is formed is inserted in the contact portion of the fixing belt and the rubber roll and heated by a heater, and, thereby, the toner image is melted and fixed on a surface of the recording medium.
According to such a belt fixing process, since, the heater directly heats only through a thin film-shaped belt, the heated portion reaches a predetermined temperature in a short time and thereby the waiting time after a power source is turned on can be cut back significantly. Furthermore, another advantage is that since only the necessary portion is heated, power consumption is small.
As a resin material that may be preferably used in various applications and simultaneously satisfies a variety of characteristics such as the heat resistance, endurance, mechanical strength, chemical resistance and electrical stability that are required over the entirety of belt members such as a transfer belt, an intermediate transfer belt and a fixing belt used for an electrophotographic apparatus and has various kinds of functions, polyimide-based resins such as polyimide and polyamideimide are most superior.
Such a polyimide-based resin is characterized in having an imide ring structure in a molecular structure thereof, and, without having a large side chain structure, having a main chain structure such as an imide ring or a phenylene group that is high in rigidity. Accordingly, the polyimide-based resin is inhibited from freely rotating in a resin molecular chain and, since there is a strong interaction force between molecular chains, high mechanical strength and endurance are realized. Furthermore, the polyimide based-resin does not have an ionic polar group, and raw materials thereof may be readily purified; accordingly, less impurities are contained and electrical stability is high.
However, when an endless belt made of the polyimide-based material such as the polyimide or polyamideimide is used as a transfer belt, a fixing belt, a transfer and delivery belt or an intermediate transfer belt, a process where a recording medium such as paper or the like is held and released on a surface portion is carried out repeatedly and continuously. Accordingly, the endless belt is required to unfailingly be released from the recording medium in the holding and releasing process.
Further, in a fixing belt, a method where, in order to secure releasability, a releasing layer low in the surface energy is disposed on a surface of a belt material to secure peelability is proposed.